The deal this week to build a new headquarters for Uber Technologies Inc. in Mission Bay closes the door on one factor that’s been driving up the price of property there – the chance to avoid San Francisco’s looming Proposition M cap on office development.

With Thursday’s announcement that Alexandria Real Estate Equities and Uber Technologies would combine to acquire and develop two Mission Bay parcels into a 422,000-square-foot headquarters for the booming transportation-dispatching tech firm, the last big office site in the area has now been snapped up.

Much of Mission Bay was entitled for development years ago, and those allocations under S.F.’s longstanding development limits have been passed along as the properties have changed hands. That’s provided certainty for developers that they’ll be able to go ahead, even if the city hits the cap imposed by Prop. M.